Multi-beam cathode ray tube character display

ABSTRACT

A multi-beam cathode ray tube having a cathode with six-sided channels defining a substantially honeycomb type structure having electron emission coatings on flat faces thereof lying in a single plane and facing the target area. Grid and anode panels having plural rows of plural apertures paralleling and alined with the flat faces form the plural beams, and a graient field helical anode eliminates divergence of the beams from each other arising from like charges.

United States Patent Standaart 1 July 24, 1973 [54] MULTl-BEAM CATHODE RAY TUBE 2,862,144 11/1958 McNaney 313/86 KM X CHARACTER DISPLAY 332338 22323 313/83 SP c esmger [76] In e to Adrian Slindflflrt, 5 Bonbmok 3,432,710 3/1969 Gumpertz 313/86 KM x Cir., Winston-Salem, NC. 27106 2 Filed; 1 1971 Primary Examiner-Robert Segal [21] A l N 172 756 Attorney-Thomas B. Van Poole et al.

[57] ABSTRACT [52] 313/70 313/86 313/86 SP A multi-beam cathode ray tube having a cathode with [51} Int. Cl H013 29/50, H01 31/16 Si Sided channels definin s bstantia hone 6 mb [58] Field of Search 313/69, 69 c, 70 R, g a u Y y type structure havlng electron em1ss1on coatings on flat 313/86 KM faces thereof lying in a single plane and facing the target area. Grid and anode panels having plural rows of [56] References Cited plural apertures paralleling and alined with the flat UNITED STATES PATENTS faces form the plural beams, and a graient field helical 2,272,165 2/1942 Varian Bl 313/69 R X anode eliminates divergence of the beams from each $1 8 other arising from like charges. is e 2,811,668 10/1957 McNaney 313/86 KM X 4 Claims, 7 Drawing Figures PATENIEUJULZMQB SHEET 1 BF 3 IN VENTOR be/A 16 5 rAA/oAAer mfl mm Mmc ATTORNEYS PAIENIEB JUL 24 I973 3. 748 514 SHEU 2 BF 3 I N VENTOR Aoemw WJrAIwAAeT' MULTI-BEAM CATHODE RAY TUBE CHARACTER DISPLAY BACKGROUND AND OBJECTS OF THE INVENTION The present invention relates in general to cathode ray tubes, and more particularly to cathode ray tubes for computer displays and other applications requiring very high writing speeds.

The use of cathode ray tubes for computer displays has created a demand for cathode ray tube writing speeds much higher than those that were readily available from previous cathode ray tube constructions, for example writing speeds up to 1200 BAUD. One approach to providing such higher writing speeds has been through use of the concept of multi-beam, single gun cathode ray tube designs. For example, one commerically available multi-beam cathode ray tube which has been marketed has seven electron beams, and certain experimental multi-beam cathode ray tubes have been provided with a still higher number of controllable beams. Two major factors which have imposed serious design problems for multi-beam cathode ray tubes are low individual beam currents and the occurrence of beam divergence arising from mutual repulsion by charges of like polarity.

An object of the present invention is the provision of a novel multi-beam cathode ray tube capable of increased writing speeds, wherein a novel cathode structure is provided to achieve uniform electron emission with maximum resistance to heat warpage and overcome low power density characteristics of multicathode systems.

Another object of the present invention is the provision of a novel multi-beam cathode ray tube construction wherein a special acceleration anode construction is employed to eliminate beam divergence otherwise resulting from the repulsion of charges of like polarity of electron beams, to permit use of a large number of beams in the cathode ray tube.

Yet another object of the present invention is the provision of a novel multi-beam cathode ray tube construction employing unique multi-grid control and beam shaping elements characterized by freedom from pre-fabrication oxidation and ability to remain stable at tube fabrication or operating temperatures.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a somewhat diagrammatic perspective view of a multi-beam cathode ray tube constructed in accordance with the present invention, with parts of the deflection yoke and focus coil broken away and parts within the neck portion of the cathode ray tube shown as visible through the glass neck portion;

FIG. 2 is a detailed section view, to enlarged scale, of the honeycomb cathode construction illustrating the design of the cathode element;

FIG. 3 is a longitudinal section view through the cathode ray tube, taken along the line 33 of FIG. 1;

FIG. 4 is a front elevation view of the cathode;

FIG. 5 is a side elevation view of the cathode assembled to the control grid, shown to enlarged scale;

FIG. 6 is a somewhat diagrammatic front elevation view of the control grid, showing the connections therefore; and

FIG. 7 is an enlarged section view through one of the holes of the control grid, taken along the line 77 of FIG. 6.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, wherein like reference characters designate corresponding parts throughout the several figures, the multi-beam cathode ray tube of the present invention is indicated generally by the reference character 10 and comprises the usual glass envelope including an elongated neck section 11 and a face plate section 12 of larger cross-section than the neck section terminating in the front face 13 carrying the phosphor target indicated in outline at 13A. The glass neck section 11 of the cathode ray tube 10 adjacent its juncture with the face plate section 12 is encircled by the usual deflection yoke 14 and focus coil 15. In the rear portion of the glass neck section 11 is the source of the electron beams, which is generally referred to as an electron gun and is indicated by the reference character 16. The electron gun in the illustrated embodiment includes a cathode generally indicated at 17, a control grid generally indicated at 18, a first anode indicated at 19 and a rectangular tubular accelerating anode 20. These elements may be preassembled on a supporting framework generally indicated by longitudinally extending frame members 21 and inserted as a unit in the neck section 11 of the cathode ray tube during manufacture.

The low power density characteristic of multicathode systems employed in some multi-beam cathode ray tubes is overcome in the present invention by employing a unique nickel cathode design for the cathode 17 wherein the cathode has the appearance of a segment of a honeycomb when viewed from the end or in section as illustrated in FIG. 2. As will be seen from FIG. 2, the cathode 17 is formed from a pair of nickel sheet members 23, 24 each having a series of five spaced parallel outwardly projecting ribs or channel formations 23A, 24A having outwardly convergent, similarly inlclined sides 23B, 24B and flat outer walls 23C, 24C paralleling the main plane of the cathode, giving the channels a truncated isosceles triangular configuration. The flat outer walls 23C and 24C of the rib or channel portions extend the full width of the cathode, and the sheets 23 and 24 are assembled at each end and between each of the elongated channel formations 23A, 24A by spotwelding, thereby providing a most rigid and stable cathode design. The filament windings are formed of spiral tungsten filaments, indicated at 25, insulated by an insulating layer of high temperature ceramic such as alumina or fused aluminum oxide. The honeycomb design provides maximum resistance to heat warpage from heating the cathode to operating temperatures, thus assuring that the cathode will remain parallel to the control grid for maximum efficiency of electron emission. The rectangular and parallel cathode surfaces 23C on which the cathode material is deposited, as indicated at 26, are of sufficient axial length, extending from one end of the cathode to the other, to assure maximum electron emission from as many as seven controllable grid apertures at a current density to enable each electron beam to develop 50 to 60 microamperes of current. The entire length of each of the channel formations 23A which include the flats 23C carrying the cathode coating is heated by the spiral tungsten filament 25. To provide high electron emission from the cathode structure, the cathode flat areas 23C are coated by spray, paint, or electrophoretic deposits of standard cathode material, such as that referred to commercially as Tri-Carbonate. This cathode coating is protected from atmosphere poisoning by a layer of organic lacquer until the cathode ray tube is activated in the final fabrication stages. The honeycomb structure herein described lends itself to rapid manufacture and ease of fabrication by machine stamping or die rolling, and when assembled by spotwelding at the ends of the sheets 23, 24 and between each cathode flat, provides a stable and rigid cathode design.

The control grid, indicated by the reference character 18, and illustrated in FIGS. 6 and 7, provides control for each individual beam intensity and current. The control grid 18 in the preferred embodiment is in the general configuration of a rectangular panel, similar to the panel or substrate for a printed circuit board, having a plurality of holes or apertures 18A arranged in rows along axes paralleling and aligned with the center axes of the five flats 23C of the cathode carrying the cathode material 26. To provide the 35 electron beams, five rows of control grid apertures 18A are provided, each row having seven control grid apertures 18A therein. The ceramic substrate, indicated at 18B in FIG. 7 is provided with the grid apertures, having an initial or unplated diameter in one example of 0.01184 inches, each aperture having a stepped entrance and exit end formed by an annular slightly larger crosssection aperture portion at the entrance and exit ends. The ceramic substrate 18B is provided with a gold plating, indicated at 18C formed by first applying an initial thickness of approximately 1,000 Angstrom units (or about one ten thousandths of a millimeter) of gold by a vacuum process known as sputtering. This sputter gold layer is applied to both surfaces of the substrate 18B and to the inside walls of the grid apertures 18A to assure firm adhesion of the metallic gold to the ceramic substrate. The control grid substrate is then electroplate to increase the thickness of the gold to 0.001 inch (or 0.025 millimeters). Alternatively, cooper may first be applied to the ceramic substrate,.after which the substrate is then electroplated with nickel to provide a thickness of about 0.001 inch.

After electroplating the control grid, it is then given a coating of a photo-sensitive etch resist, such as Eastman Kodak Companys KPR or KMER or KTFR resist. This photo-sensitive etch resist is then exposed to a precision glass photographic plate containing a negative image of the control apertures and their attachment metal paths, and the resist is then processed in accordance with the manufacturers recommeda tions for the type of resist employed and is etched in an Aqua Regia solution composed of one part hydrochloric acid mixed with three parts nitric acid for etching away the unwanted metal gold. Alternatively, the unwanted metal gold can be etched away by a solution of sodium cyanide containing hydrogen peroxide or by electrolytic etching with alkaline cyanide solutions and a steel cathode using six volts D. C. power.

The first anode 19 is similar to the control grid 18, in that the ceramic substrate 19B may be of the identical size and design as the control grid substrate and is likewise provided with 35 apertures 19A. However, whereas the control grid 18 contains 35 individual conductive attachment paths 18C leading to grid connections at the edges of the control grid, the first anode 19 has the surface facing away from the control grid or toward the target provided with a layer of metal gold like the one provided on the control grid before etching, the layer of metal gold on the first anode being broken only by the beam apertures 19A. The other surface of the first anode 19, which faces the control grid, contains no gold except for a rim around the apertures about 0.001 inch wide. Each of the control grid 18 and first anode 19 may be about 1.5 millimeters in thickness.

To eliminate inherent beam divergence by the repulsion of the like charges of the negative electron beams, the cathode ray tube is provided with a gradient field helical anode 28 provided in the neck section 11 between the conventional rectangular tubular accelerating anode 20 and the forward end of the neck section. The gradient helix 28 is formed as a two millimeter conducting path extending in a helical pattern along the inside wall of the glass neck 11 of the cathode ray tube in encircling relation to the electron beams and having such resistance and composition as to exhibit a drop in potential of about 14,000 volts over the total length of the helix 28. The helix 28 thus has an overall resistance of approximately megohms at full beam current of 50 microamperes for each of the 35 individual beams. The end of the helix nearest the cathode, in one embodiment, is connected to minus 24,000 volts D. C., with the first anode 19 connected to about minus 24,000 to minus 24,500 volts D. C. and the cathode connected to about minus 24,000 volts D. C.. The graduated intensity of negative high voltage surrounding the electron beam paths through the cathode ray tube from the cathode to the target eliminates the normal beam divergence arising from repulsion of like charges of the beam. The helix potential is at a maximum negative potential at the cathode end of the helix, where the electron velocity of each beam is slowest and the beam divergence is maximum. This negative potential of the helix 28 gradually diminishes toward the target area and simultaneously the electron speed increases to require lessnegative potential to maintain beam alignment. The helix anode terminates with a junction with a metal distortion correction anode, schematically indicated at 30 in FIG. 3, connected to a potential of about minus 10,000 volts D. C., to eliminate pincushioning or barrel distortion typical of 70 deflection systems.

By the above described construction, employing the honeycombed type of cathode structure providing five elongated cathode flats carrying the cathode material, in association with the control grid and first anode elements having five rows of seven apertures cach aligned with the cathode material flats of the cathode, an advantageous design is provided for a cathode ray tube having as many as 35 controllable beams. By virtue of having 35 independently controlled electron-beams within the cathode ray tube envelope, the cathode ray tube will contain a maximum of 35 times the writing speed of conventional single electron beam cathode ray tubes and five times the writing speed of existing multibeam cathode ray tubes. The honeycombed cathode construction provides uniform electron emission and minimum cathode distortion from filament heat. The

control grid 18 and first anode l9 employing metallic gold provides a non-oxidizing or tarnishing metal conductor capable of maintaining excellent conductivity through fine lines and provides freedom from prefabrication oxidation and ability to remain stable at tube fabrication or operating temperatures. The gradient helical accelerating anode 28 provides means for elimination of the inherent divergence of multielectron beams arising from repulsion of like charges.

What is claimed is:

l. A multi-beam cathode ray tube construction for producing a matrix display pattern from plural electron beams arranged in plural rows and plural columns to generate display images of alpha-numeric characters formed from spot elements of the matrix pattern, comprising a glass envelope including an elongated generally cylindrical neck section and a face plate section jointed thereto having a phosphor target; a single electron gun within the rear region of said neck section including a cathode for emitting electrons, beam control and shaping perforated electrode means having plural rows of plural holes for controlling and shaping the electrons emitted by said cathode into plural rows of plural beams to form the matrix pattern, each of said holes being lined with conductivematerial connected by conductor strips to terminals for applying selected potentials to the lining material; and accelerating anode means for accelerating the electrons in said beams toward the target to form a spot image on the target for each of the beams, said anode means including a gradient field helical anode formed of a narrow band of resistance material extending in a helical path along said neck portion in encircling relation to the electron beams over the major portion of their paths from the electrode means to the target area, said cathode comprising a pair ofjoined metallic sheet members each having a plurality of outwardly projecting truncated V-shaped formations collectively defining plural six-sided channels of substantially honeycomb configuration in side elevation defining plural flat faces in a single plane spanning the width of the cathode in parallel respectively alined relation with the rows of holes and beams, the channels housing coiled filament wire along the length thereof closely conforming to the cross-section of said channels, and said flat faces each having a coating of electron emission material which is thermally activated to emit electrons to form said beams.

2. A multi-beam cathode ray tube construction as defined in claim 1, wherein said electrode means includes a control grid formed of a rectangular substrate panel having rows of scud holes therethrough alined respectively with said flat faces, said panel and said flat faces lying in a pair of parallel planes.

3. A multi-beam cathode ray tube construction as defined in claim 2, wherein sand material lining said holes and said conductor strips are gold plated on the control grid substrate.

4. A multi-beam cathode ray tube construction as defined in claim 1, wherein said helical anode is a helical conducting path exhibiting a potential drop of about 14,000 volts over the total length of the helix.

pate t 3,748,514 Dated July 24, 1973 lnventor(s) ADRIAN STANDAART It is certified that error appears in the above-identified patent and that said Letters Patent are hereby Corrected as shown below:

On the fro nt page, in the ABSTRACT, at line 7, "graient" should read -gradient.

Signed and sealed this 9th day of April 1971;.

(SEAL) Attest:

EDWARD I I.FLETGHER,JR. C. MARSHALL DANN Atte sting Officer Commissioner of Patents F ORM PO-1050 (10-69) I USCOMWDC wandug [1.5. GOVERNMENT PRINTING OFFCE I I9, 0-355-33. 

1. A multi-beam cathode ray tube construction for producing a matrix display pattern from plural electron beams arranged in plural rows and plural columns to generate display images of alpha-numeric characters formed from spot elements of the matrix pattern, comprising a glass envelope including an elongated generally cylindrical neck section and a face plate section jointed thereto having a phosphor target; a single electron gun within the rear region of said neck section including a cathode for emitting electrons, beam control and shaping perforated electrode means having plural rows of plural holes for conTrolling and shaping the electrons emitted by said cathode into plural rows of plural beams to form the matrix pattern, each of said holes being lined with conductive material connected by conductor strips to terminals for applying selected potentials to the lining material; and accelerating anode means for accelerating the electrons in said beams toward the target to form a spot image on the target for each of the beams, said anode means including a gradient field helical anode formed of a narrow band of resistance material extending in a helical path along said neck portion in encircling relation to the electron beams over the major portion of their paths from the electrode means to the target area, said cathode comprising a pair of joined metallic sheet members each having a plurality of outwardly projecting truncated V-shaped formations collectively defining plural six-sided channels of substantially honeycomb configuration in side elevation defining plural flat faces in a single plane spanning the width of the cathode in parallel respectively alined relation with the rows of holes and beams, the channels housing coiled filament wire along the length thereof closely conforming to the cross-section of said channels, and said flat faces each having a coating of electron emission material which is thermally activated to emit electrons to form said beams.
 2. A multi-beam cathode ray tube construction as defined in claim 1, wherein said electrode means includes a control grid formed of a rectangular substrate panel having rows of scud holes therethrough alined respectively with said flat faces, said panel and said flat faces lying in a pair of parallel planes.
 3. A multi-beam cathode ray tube construction as defined in claim 2, wherein sand material lining said holes and said conductor strips are gold plated on the control grid substrate.
 4. A multi-beam cathode ray tube construction as defined in claim 1, wherein said helical anode is a helical conducting path exhibiting a potential drop of about 14,000 volts over the total length of the helix. 